Gold Nugget 1.495 OZT - No Aqua Regia 99.67% fine _inquart_

kadriver · Jul 30, 2012

Hello:

I have recently started using careful inquartation and dilute nitric acid treatments only to refine my gold.

I avoid the aqua regia and SMB precipitation steps completely.

I carefully test the karat scrap gold that I am going to refine and then add just enough silver to get as close as possible to 6k after inquartation.

I then treat the inquarted 6k gold with up to four, 50/50 (68% nitric acid/distilled water) dilute nitric acid treatments until the last treatment is nearly colorless.

I use the resulting silver nitrate solutions to dissolve more scrap sterling & 925 silver scrap.

The last treatment (which is nearly colorless) is saved and used to do the next batch of inquarted karat scrap.

I have been getting any where from 993 to 998 fine gold nuggets by using this method.

It saves time and effort - I do only my own gold bound for sale to the refiner - in this case NTR Metals.

Included in this post are some pictures of the last nugget I produced using the method described above.

Thanks for looking - any critique is welcomed.

kadriver

nickvc · Jul 31, 2012

Many asian jewellers use exactly this method to refine their scrap the difference been that they have 20-24 karat scrap as the starting material and traditionally used copper to inquart not silver but they are rarely worried about PGMs in the mix and the alloys are usually copper or copper and silver.

Harold_V · Jul 31, 2012

If memory serves, Hoke mentions this process in her book. The only real problem I can see is that it offers the (minor) risk of leaving behind contaminants that have the potential to ruin gold's ductility. For the purpose stated, it's more than good enough, however.

I suggest turning out the finest quality possible only because in doing so, you do not limit the potential customer. If jewelers in one's area become aware of a competent (local) refiner, the door opens to picking up customers, as well as opening a door for the potential sale of fine gold at spot price. That was the very basis of my operation, and proved to be a wise decision. That may or may not be true today, considering small refiners did not exist when I started refining (due to federal regulations on gold).

Harold

goldenchild · Jul 31, 2012

Harold_V said:
If jewelers in one's area become aware of a competent (local) refiner, the door opens to picking up customers, as well as opening a door for the potential sale of fine gold at spot price. That was the very basis of my operation, and proved to be a wise decision. That may or may not be true today, considering small refiners did not exist when I started refining (due to federal regulations on gold).

Harold

I find that the biggest barrier in getting jewellers as clients is trust. Even more so when you don't have a brick and mortar operation. When you tell someone you do this stuff out of your garage it usually gets you raised eyebrows and facial expressions of doubt. Add the fact that there is a saturation of refineries not too far away (NY) and it makes it very difficult to get clients that are willing to work with you.

goldsilverpro · Jul 31, 2012

kadriver,

About 10-15 years ago, a company in Italy, I believe, sold a karat gold refining unit based on inquartation with copper. I'm thinking they used a series of 3 or 4 hot nitric leaches that were progressively made stronger, sort of like the way Au/Ag assay beads are parted. I think they claimed a final gold fineness of at least 999 and maybe 999.5, without the use of AR.

You might raise the purity even more by using a stronger (say, 2:1) hot nitric at the end.

kadriver · Jul 31, 2012

GSP:

I will try using 2 to 1 dilution (2 nitric to 1 DH₂O) - thanks for the tip.

I use only water washes between nitric treatments - I save the wash water and add it to the silver jar.

After the final nitric treatment I wash several times with distilled water and save the water to the silver jar.

I pour off a small amount (about 10 or 15 ml) of the wash water and add 1 ml of HCl and let it stand for 60 seconds.

If there is any silver in the wash water, then the sample will produce a slight cloud of silver chloride so I repeat the wash and re-test.

Upon getting a clear HCl test, I rinse one more time, then put the gold in a casserole to dry and then melt.

I only sell to the refiner and he will just add my nugget to one of his batches for further refining.

kadriver

samuel-a · Jul 31, 2012

kadriver, are you keeping the gold 'sponge' intact while leaching and washing?

kadriver · Aug 1, 2012

Samuel

The resulting gold "sponge" retains its original shape and size from the "corn flakes" produced by pouring the molten inquarted gold into a 3 gallon stainless container of cold water.

There is no suspended powder to deal with and no settling (that I can see) from the washes. I think this is a result of "proper inquarting".

In the past, I have added too much silver and the gold will fall apart and make a fine powder that takes a long time to settle.

I pour in the wash water (distilled), give it a good swirl or two, let it all come to dead still inside the container, then pour it off and repeat to colorless.

I am going to use GSP's recommendation to use 2 to 1 dilute nitric as the final treatment on my next batch to see if I can get the purity to increase.

By the way, each of the nitric treatments last for at least an hour (sometimes 2 or 3) and the acid is boiled vigorously during these treatments.

As a caution, I have gotten some popping of steam bubbles in the reaction vessel during the final boil.

This tendency may increase while using the greater (2 to 1) concentration of nitric acid.

kadriver

kadriver · Aug 1, 2012

Also, please note that I have seen some very very fine gold dust settle from time to time on the bottom of the poured off silver nitrate from the first nitric acid treatments.

It settles a thin line around the bottom of the silver nitrate container - so there is a tiny fraction (from time to time) of very fine powdered gold that comes off the inquarted gold during this process.

kadriver

HAuCl4 · Aug 1, 2012

4metals wrote:I got the method 2 years ago from a sterling refiner processing 30,000 ounce batches, we scaled down to 1000 ounces a day because we melt 350 ounces of karat gold scrap in with the 1000 ounces of silver (essentially inquarting) and digest the alloy in 50% nitric. The gold doesn't react and is filtered out and cleaned up in another nitric dissolve and melted with a borax, soda ash, manganese dioxide flux which scavenges any remaining silver and produces a 999.5 fine bar consistently.

Courtesy of 4metals: Flux to get approx. ~9995 gold after silver inquarting + nitric.

This is the formulation for the flux to scavenge silver and base metals.

Gold Melting Flux
This is for gold from the nitric parting process

2 pounds Anhydrous borax glass (no waters)
1 pound Soda Ash
1 pound Diatomaceous earth (silica)
1 pound Manganese Dioxide
¼ pound Fluorspar (calcium fluoride)
¼ pound Calcium oxide (CaO, Lime, Type S, Unslaked)

Premix all of the ingredients and store it in a closed container. It is anhydrous and will pick up moisture from the air which will make it spit.

Add equal volume of gold sponge to flux and premix before melting.

HAuCl4 · Aug 1, 2012

Also, if you have an induction furnace and a zirconia crucible, you simply superheat the melt to 2,200 C for 10-15 minutes, and all the silver evaporates, the other contaminants oxidize and vaporize, and because you are very clever you catch any possible evaporating gold in a zirconia wool placed above the crucible. 9999 easy if no platinum group is present.

No, I don't have pictures. :lol:

Lobby · Aug 1, 2012

The problem you have with this is that you're completely at the mercy of the refiner's XRF analysis. Note that your refiner only lists the Au content in their report.

Do you think the refiner has the appropriate standards in their XRF to accurately measure gold at those purities? Since most of the karat gold they buy is around 50% gold, they concentrate their standards at those compositions.

I've taken 99.99 refined gold to various refiners in the area. I've gotten results ranging from 99.99% to 99.1% to 103% (his machine was off). It had gotten to the point where if I took some 4 nines gold to a refiner, I took a gold panda or a credit suisse bar with me to compare results.

"I've got my own standards," one refiner sniffed at me. :mrgreen:

That said, being 1% off on a 1.5 oz pure bar is only $24 (@ $1600 per oz), so as long as you're getting analytical results at those levels, go for it!

kadriver · Aug 1, 2012

Lobby;

Thanks for the info.

I do a calculation before I take them the metal.

They are usually within 2 or 3 dollars, sometimes under, other times over.

I feel they are treating me fairly.

In this example, if my button was four nines fine (.9999) and they only paid on .9967 then the difference would be .0032

.0032 X $1605 spot = $5.14 loss.

Of course I would be pushing it to believe that my button was in fact four nines fine.

kadriver

vyper · Dec 13, 2012

ka - you could try fluxing with small amounts of potassium nitrate to remove the impurities.

muconium · Apr 30, 2013

This is my first post. I've been getting practice with inquarting jewelry scrap and am getting ready for the nitric washes, per Kadriver's method here. It seems like a great way to get my feet wet!

My question: Could not the final nitric wash be in undiluted, 70 percent, nitric acid? Would that not be doing all one could to ensure thorough removal of all base metals?

Geo · Apr 30, 2013

Surprisingly, diluted acid attacks base metal faster than concentrated. I suppose it would make little difference about concentration as long as you continue the wash and rinse process until both wash and rinse stays clear.

srlaulis · Apr 30, 2013

Here is what Ms. Hoke teaches:

"Diluted acid is more efficient per unit of acid in the sense that it
wastes less of the brown gas which is an active part of the reaction. But
it works less rapidly. However, the matter is not as simple as it appears,
because as soon as the acid starts to work it begins to dilute itself. Since
the concentration changes every second, it seems idle to be too dogmatic
about the exact concentration at the start.
The concentrated acid sometimes works so rapidly that it boils over;
this tendency may be reduced by adding water. Frankly it is hard to say
how much water to add, because this tendency to boil over is dependent
upon the size of the pieces of metal as well as upon the number of them,
and these factors change with every batch.
If you use much water you increase your acid efficiency but decrease
the speed of operation, and you have more liquid to filter and store.
Some workers use ten parts of water to one of acid; others use ten parts
acid to one part water. The results are the same in the end. We ourselves
use about equal quantities of water and acid."-C.M. Hoke, Refining Precious Metal Wastes

Steven

kadriver · May 22, 2013

muconium said:
This is my first post. I've been getting practice with inquarting jewelry scrap and am getting ready for the nitric washes, per Kadriver's method here. It seems like a great way to get my feet wet!

My question: Could not the final nitric wash be in undiluted, 70 percent, nitric acid? Would that not be doing all one could to ensure thorough removal of all base metals?

I have used concentrated nitric treatments but there is a tendency for popping in the reaction vessel causing hot acid and gold to spit all over the place if you're not careful. Using dilute nitric seems to eliminate popping all together.

Another factor is the time spent in the boiling dilute nitric acid. I have left the gold in for several hours and this seems to make for better purity at assay.

Using straight concentrated 68-70% nitric would be like using just dish soap (with no water) to wash your hands. It would get your hands clean, but adding water makes the dish soap work more efficiently.

I have stopped using concentrated nitric and always use dilute when doing these treatments.

The gold buttons turned in to the refiner have been consistent .998 at assay.

Processing the gold this way saves much time and effort, especially if it is destined for sale to the refiner.

But I always do a complete refining every now and then to maintain proficiency - or else I'll forget how to do it!

I really like doing a double refining using two different dissolutions and precipitations.

Usually first dissolve the recovered inquarted gold in AR and precip with SMB, then dissolve again using chlorine gas and precip with oxalic acid.

This double refining makes a gorgeous piece of pure gold with no traces of contamination. Gold refined this way has given 99.99 at assay from the refiner.

kadriver

4metals · Apr 29, 2015

The moderators would like to thank all of the members that contributed to the original thread that this post was based on, as well as those that asked questions showing what was missing. Because of the extra length and interest in this thread we have created the above consolidated version making for an easier read. We encourage all members to read, comment, and ask questions in the original thread, Gold Nugget 1.495 OZT No Aqua Regia 99.67% fine

The moderators have edited some posts in this thread that made reference to posts that were deleted. We strive to make these Library threads as concise as possible by deleting posts that do not add information to the original topic. All of the original posts are still preserved in the thread listed above.

The Library threads should not be considered to constitute a complete education. Instead, they're more like reading a single book on the subject of recovery and refining. There is so much more information on the forum, and it is impossible to include it all in these condensed threads. Members are strongly encouraged to read the rest of the forum to round out their education.

For those who prefer a printed copy, a pdf file of this thread is provided below.

Gold Nugget 1.495 OZT - No Aqua Regia 99.67% fine _inquart_

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